1. Field of the Invention
The invention relates generally to an electrode for plasma generation and more particularly, to a plasma processing apparatus.
2. Description of the Related Art
The capacity and functions of semiconductor devices has recently increased with improvements in semiconductor device integration. More semiconductor devices have been formed on a limited size wafer, and the pattern sizes for semiconductor devices have been decreasing in size.
To achieve the improved device integration, ionized process gas (i.e., plasma) has been utilized in semiconductor device fabrication. Specifically, plasma dry etching is used to pattern semiconductor devices. The etching gas in the plasma state contains ions, electrons and radicals.
The plasma dry etching apparatuses for manufacturing semiconductor devices can be divided according to the construction of electrodes to form the plasma and the usage of a magnetic field. For example, the etching apparatus may be a RIE (Reactive Ion Etching) apparatus, a MERIE (Magnetically Enhanced Reactive Ion Etching) apparatus, a CDE (Chemical Downstream Etching) apparatus, an ECR (Electron Cyclotron Resonance) apparatus, a TCP (Transformer Coupled Plasma) apparatus, etc.
FIG. 1 schematically shows a conventional plasma dry etching apparatus. Referring to FIG. 1, the apparatus contains a process chamber 10 for performing dry etching by plasma which is generated by ionizing a supplied process gas.
The process chamber 10 contains a gas supply line 12 to supply a process gas into the process chamber 10. A vacuum line 14 to form a vacuum inside the process chamber 10 is provided on the lower side of the process chamber 10. A vacuum pump 18 is connected to the vacuum line 14 to perform pumping. A valve 16 is provided on the vacuum line 14 to control the pressure inside the process chamber 10.
In addition, a lower electrode 20 is provided inside the lower portion of the process chamber 10. A wafer 22 to be etched is mounted on the lower electrode 20. An upper electrode 24 is provided in the upper portion of the process chamber 10. High frequency power is applied to the lower electrode 20 from a high frequency power source 28. The power is supplied to the lower electrode 20 through a matching box 26. The high frequency power source 28 and the upper electrode 24 are both grounded.
The etching apparatus operates as follows. First, the valve 16 installed on the vacuum line 14 is opened and the inside of the process chamber 10 is evacuated to a high vacuum state by the operation of the vacuum pump 18. Then, a process gas such as CF4, HBr, Cl2, Ar, etc. is supplied into the process chamber 10 through the gas supply line 12.
Then, when the high frequency power source 28 applies a certain high frequency power to the lower electrode 20, an electric field is formed inside the process chamber 10 between the lower electrode 20 and the upper electrode 24. The lower electrode 20 emits electrons which are accelerated with kinetic energy by the electric field into the process gas. The electrons passing through the process gas impart energy to the process gas by colliding with the process gas atoms or molecules. The energized process gas is ionized so as to form ions. The ions are then accelerated by the electric field. The ions pass through the process gas and collide with and ionize further process gas atoms or molecules to generate a plasma state having positive ions, negative ions and radicals.
The positive ions and the radicals from the plasma impinge on the surface of the wafer 22 and etch a certain portion of the wafer. Hence, the wafer 22 is patterned by dry plasma etching. However, the conventional plasma etching process suffers from the problem of non uniform etching over the whole area of the wafer 22. As shown in FIG. 2, the plasma density is constant in a certain region around the center of the process chamber 10. However, the plasma density decreases toward the edges or peripheral portion of the process chamber. Therefore, the plasma density is non uniform throughout the process chamber.
The non uniform plasma density adversely effects the etching uniformity of the wafer. For a large diameter wafer, such as an 8 inch or a 9 inch wafer, the etch rate at the edge of the wafer is lower than the etch rate at the c (enter of the wafer, which results in an etch failure around the edge of the wafer (i.e., the peripheral areas of the wafer are insufficiently etched which results in formation of defective devices at the periphery of the wafer).
In addition, the value of the plasma density formed inside the process chamber is related to the values of high frequency power and the surface area of the electrode. However, the surface area of the electrode is limited by the placement of other parts inside the process chamber. Therefore, there is a limit on how large the electrode may be made to increase the plasma density. The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.